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Repair and disassembly guides for guitar amplifiers.

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Change xlr speaker outs to 1/4" speaker outs?

This vibration technologies sl140 is a solid state slave amp. There are two xlr (microphone) cable speaker outs that I want to switch to 1/4" jacks.

The 1/4" jacks have three pins on the back.

The xlr jacks are also connected by three wires to the circuit board.

The xlr jacks also come out of the amp as 8 ohm and 16 ohm and are wired accordingly within(3 wires).

I understand I only need two wires (+ and -) to wire up the 1/4" jacks and I'm handy with a voltmeter to determine what pins are center or not but the xlrs and internal wiring of the amp are throwing me.

My thoughts are two of the wires are the same (either hot or ground) and the lone wire will be the other. Determining which is hot or ground in the amp is a problem.

The wires are colored and I am planning on opening up to see the board and what's what but was kind of hoping for someone who may know a thing or two to throw a bone my way. I was hoping it would be quite easy to do.

(Couldn't find a schematic, info or an active number for this company.)

Thanks

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joe, since this seems to be a somewhat different piece of hardware, it might be beneficial to post a couple of images on here so we can see what you see.:-)

Thanks very much for the background and help...I just got into the amp...which is just the slave amp...it has an input on the front with a gain as well but no distortion effect I think...it is grey. ;)

Here's some pics just in case as I wouldn't want to miswire this thing...it seems the two yellow are continuous with the screws in the back plate, not the plate itself, as well as the casing of the xlr outputs.

It appears that I have ground(?) to pin 1 and 2 on both xlrs but they head out to different spots on the board near one another and the 8ohm tap has it's grounds separated.

Pin 3 seems to go into the other side of the board and is common on both 8 and 16 taps.

Thanks again!

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joe, a bit of history on these amps "Vibration Technology was a company founded by Hari Ghandi and operated in the 70's and early 80's in Ontario. Hari didn' want his circuits stolen so he used unmarked components in many places and didn't issue schematics to the public, or even techs, he figured they were well enough made that they wouldn't break down and repairs would be unnecessary. The biggest problems with these amps were all the aluminum parts that gradually oxidized , particularly pots that were grounded to the aluminum chassis, but a simple cleaning would usually solve the problem. The entire 140 series used the same power amp, it was connected by a 9 pin plug to the various models of pre-amps which were mounted to the front of the cabs. Hari used his own design for the distortion effect, and no matter what was said to him, he would not change it. Most people didn't like the sound, and this was the greatest criticism of his amps. on the other hand there was no shortage of pedals available and the amps themselves were solidly made. The cabs were solid and lasted forever, even using less than premium quality speakers. The biggest drawback to VT, though, was that they wee gray, and during the hayday of heavy metal, everyone wanted black." from here. While I am waiting to see if I get a manual for the SL140, but I do have the one for the VR-140. Just want to determine the difference in wiring. I attached an image ( from here) of the pinout of the XLR to various other adapters. Hope this helps. Good luck.

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You will need to determine if the outputs are balanced or not, it seems strange that they made speaker outputs with XLR, this would make me thin they are lineout rather than speaker out level. Post some pics and I can help you with this.

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